Commercial two-electrode lithium ion batteries for supplying power to electric and hybrid vehicles are commonly adapted to enable monitoring of battery state-of-health (SOH) and/or state-of-charge (SOC) by installing various sensors at the battery. However, in two-electrode systems, only relative measurements between the working electrodes can be determined. Three-electrode lithium ion batteries, which incorporate a reference electrode into the battery, can provide a more accurate assessment of battery state-of-health and/or battery-state-of-charge since absolute measurements of each working electrode can be obtained. Reference electrodes are either installed during manufacture of a new battery, or existing two-electrode batteries may be retrofitted with a reference electrode.
For example, Fulop (US 2012/0263986) discloses a lithium rechargeable cell with reference electrode for SOH monitoring, wherein a reference electrode comprises active material deposited on a metal current collector, or mixed as particulate with binder and a conductive additive and then coated on a metal foil. The reference electrode may be electronically connected to the can. Furthermore, in cases where the can is aluminum, copper, stainless steel, or titanium, the can is capable of serving as the reference electrode, wherein the interior wall surface of the can is coated with protective insulating material to provide electronic insulation of the can from the working electrodes.
The inventors herein have recognized potential issues with the above approaches. Namely, conventional methods of installing reference electrodes during manufacture of new batteries can be costly and complex, since an additional battery port must be added and properly sealed to accommodate the reference electrode. Furthermore, addition of the reference electrode may reduce the battery capacity for a given size since the reference electrode, and associated seal, port, separator, etc. consume volume that may be otherwise used for active battery material. Further still, conventional methods of retrofitting two-electrode batteries with a reference electrode involve breaching the sealed can of the battery, which can be costly and can often damage the battery components, leading to premature battery failure. Further still, the aluminum, titanium, copper, or stainless steel can reference electrodes of Fulop are not stable non-polarizable reference electrodes that can accurately measure absolute potentials of each working electrode. Further still, mixing particulate with binder and a conductive additive and then coating the mixture on a metal foil is a complicated multistep, multicomponent method of forming a reference electrode that reduces manufacturing efficiency and increases manufacturing costs.
One approach that at least partially overcomes the above issues and achieves the technical result of manufacturing a reference electrode in an existing sealed battery is a method of manufacturing a reference electrode for a lithium ion battery, comprising charging the battery to a threshold state-of-charge, where the battery includes a neutral metal can and a negative electrode, and plating a reference electrode on an interior surface of the can by electrically connecting the neutral metal can to the negative electrode, wherein a neutral metal can potential is greater than a negative electrode potential. In this way, it is possible to retrofit existing two-electrode batteries to form the reference electrode without breaching the seal of the battery, and to manufacture reference electrode for lithium ion batteries in a more cost-effective and less complex manner, as compared with conventional methods. Furthermore, a stable, non-polarizable reference electrode can be provided for accurately monitoring SOH over the life of the battery.
In another embodiment, a lithium ion battery comprises a neutral metal can, and a reference electrode electroplated on an interior surface of the neutral metal can. In another embodiment, a vehicle battery management system comprises a lithium ion battery including a neutral metal can and a reference electrode electroplated on an interior surface of the neutral metal can, and a controller with executable instructions to determine a state-of-health of a battery by measuring a potential difference between the reference electrode and a negative electrode, and measuring a potential difference between the reference electrode and a negative electrode.
In another embodiment, the reference electrode may be manufactured by connecting the neutral metal can and an electrode of the lithium ion battery with an electrical power source, and directing current from the electrical power source to the neutral metal can.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.